Asthma is a relatively common disorder in pregnancy (4 percent) with the potential to increase maternal and fetal morbidity. As with all medical disorders in pregnancy, the usual pharmacologic management is a source of concern for mothers and health care providers. Yoga therapy has been shown to improve asthma as measured by pulmonary function tests, symptom scores, and frequency of asthma attacks in nonpregnant women and men. The study proposed, which is ancillary to the ongoing observational study of asthma in pregnancy, is a pilot study to investigate the efficacy of yoga to improve the pulmonary function in asthmatic women during pregnancy. The design is prospective, single blinded, randomized, and placebo-controlled. Moderate to severe asthmatics who are candidates for the observational asthma study will be randomized to either a yoga program, a non-yoga program of relaxing for the same amount of time, or a non-intervention arm. Pulmonary function tests, frequency of asthma exacerbations, and medication usage will be measured at each office visit. The primary outcome will be a 20 percent improvement of peak flow rate as determined by analysis of variance in subjects who perform yoga as compared to control subjects. The study is designed as an intent to treat trial, however compliance will be assessed by a prospectively gathered diary which will be blinded until the end of the study.